Electronic microwave switch



Oct 1957 P. J. ALLEN ELECTRONIC MICROWAVE SWI'TCH Filed Oct. 8. 1952 CURRENT SUPPLY AND REVERSING SWITCH I'IH L GYRATOR 25 GYRATOR United States ELECTRDNIC MICROWAVE SWTICH- Philip J. Allen, Forrestville, Md., assignor to the United States of America as represented by the Secretary of the Navy This invention relates generally to microwave switches, and more particularly to electronic microwave switches.

Many difficulties attend the problem of performing a switching action in microwave waveguide circuits. Because of the unusual shapes common to waveguide cir cuits, switching elements must provide compatible shapes to minimize insertion losses. Because of the high power handling abilities of waveguide circuits it is accordingly desirable that waveguide switching elements be likewise able to handle high power. it is further desirable that microwave switches be controllable electronically for rapid or automatic operation, which cannot be accomplished satisfactorily with mechanical switching devices.

It is therefore an object of this invention to provide a microwave waveguide switch capable of handling high power at a high switching frequency while introducing little insertion loss and not requiring mechanical motion.

It is a further object of this invention to accomplish a switching action by an instantaneous phase reversing action.

It is a further object of this invention to provide a switching action by electrically controlling the magnetic field of a microwave gyrator;

it is a further object of this invention to provide unique switching actions through the combination of microwave gyrators and hybrid junctions in waveguide circuits.

Other features and advantages of this invention will be apparent from the following description and accompanying drawings in which similar characters of reference designate similar elements throughout the several views.

In the drawings, Figure 1 is an isometric View of a representative embodiment of this invention;

Figures 2a and 2b are vector diagrams explaining the operation of a portion of Figure 1;

Figure 3 is a schematic diagram of a variant embodiment of this invention; and

Figures 4 and 5 are isometric views of variant embodiments of a portion of Figure l.

Briefly, this invention divides microwave power into two equal components by means of a hybrid junction. These equal components are applied to two arms of a second hybrid junction where, if arriving in phase, they will combine and leave together through a third arm of the second hybrid junction. However, if the two components of microwave power are applied out of phase they will recombine and leave via a fourth arm of the second hybrid junction. A microwave gyrator is inserted in one of the arms connecting the two hybrid junctions. It has been found that by electrically reversing the magnetic field of the nucrowave gyrator, the relative phase of the microwave power reaching the second hybrid junction may be effectively shifted 180. Further, by inserting a second microwave gyrator in the other connecting wave-guide arm, more complex switching may be obtained.

Referring now to Figure 1 in detail, a first hybrid junction of the magic-T type is shown at 6 having horizontally opposed arms 7 and 8, a third horizontal T arm or sum terminal 9, and a vertical arm or difference terminal atent O Patented Oct. 8, 1957 10. Associated with it by waveguide sections is a second magic-T type hybrid junction 11 having a pair. of opposed horizontal arms 12 and 13,, a third horizontal arm or sum terminal 14, and a vertical arm or dilference terminal 15. Arms 8 and 13 of these hybrid junctions are shown connected together through a section of rectangular waveguide 16. Arms 7 and 12 are connected together through rectangular waveguide sections 17 and 18, this latter connection being completed. through a microwave gyrator element 19;

The microwave gyrator element 19 is of typical form and consists of a short section of circular waveguide 20 in which a small cylindrical core 21 of ferrite material is axially suspended by a coaxial cylinder 21a of dielectric material such as Teflon. A concentric coil of wire 22 is wound around the outside of the circular waveguide 20 and serves as a means for producing a controllable axial magnetic field in the ferrite core 21. The microwave gyrator depends for its operation on the magnetooptical properties of the ferrite core. A variation in the magnetic flux through the ferrite core causes a variation in the propagation characteristics of the gyrator as a microwave element. Coil 22 has its terminals connected to a current supply and reversing switch indicated generally at 23. Element 23 need be nothing more than a battery and a switch suitable to reverse the flow of current through coil 22. In Figure 1 the sum and difference terminals indicated at 9, iii, 14 and 15 of the hybrid junctions 6 and 11 are shown unconnected and may be utilized as input, output, or open terminals in accordance with the type of switching action desired. Representative switching actions available from this invention will be further described below.

To better understand the operation of this invention, an explanation of the functions of the microwave gyrator herein utilized is desirable. Accordingly, reference is now made to Figures 2a and 2b. In these figures the microwave gyrator element 19 is shown in more or less schematic form so that the direction of current fiow through the coil 22 may be indicated. For this purpose the current supply and reversing switch 23 is shown as a pair of opposite polarity batteries 28 and 29 selectably connected by switch 24 to coil 22, and in addition turns of the coil 2.2 are individually shown so that the effect of the direction of current flow on the direction of the magnetic field may be portrayed. In Figure 2a the coil is connected to battery 29 and a vector designated E1 is shown vertically disposed representing a plane polarized wave entering the gyrator from the left. At the right of the gyrator this same wave is shown by vector E01 whose plane of polarization has been shifted through an angle +0, which in the example indicated has been made In Figure 2b the coil is connected through switch 24 to battery 28 having reversed polarity, thereby reversing the current through coil 2.2. The same vector E is shown entering the left of the gyrator but it will be noted that in Figure 2b the plane of polarization of the exiting vector E02, is shown shifted by an equal and opposite angle -19. It follows therefore, that if the output from gyrator 22 may have its plane of polar ization shifted by a total of by reversing the current through coil 22, when the phase of the wave passed through the gyrator has in effect been shifted 180 by the reversal of the coil current.

It will be seen from Figures 2a and 21'; that, when 19 and 6 each equal 90, in order to pick up each output vector at full strength, the input and output rectangular waveguides most be oriented such that their E-planes are at right angles in order that the E-plane of the output waveguide will be parallel to the E-plane of the output energy. If the orientation is not 90, the transfer of energy from the gyrator will not be maximum, however,

since the reduction of energy transfer is a sinuous function of the departure from 90 orientation, small departures will have negligible eifect. However, substantial departures may cause unequal outputs between the two switch conditions.

It will be further observed from the vectors shown in Figures 2a and 21'), that the electric reversal of the magnetic field in the gyrator produces an instantaneously complete reversal of phase, since in the process of changing from the demonstrated by vector E01 to that demonstrated by Fez, the vector does not rotate through 180 but instead of collapses to zero magnitude and then expands to maximum in opposite sense. Hence tie phase reversal and the switching actions produced by this invention are instantaneous and complete.

Although the polarizat rotation angles +9 and 6 have been shown as 90 ll Figures and 222 for illustrating the desired 180 phase shift, following the teachings of this invendon the angle B may depart considerably from 90 without seriously impairing the operation of this invention. it is necessary that the input and output waveguides for the gyrator, designated 17 and 23 in Figure 1, be rectangular waveguides which will support only the TE1,0 mode. Since the output waveguide 13 will support only the Ting) mode, this waveguide will be excited only by that component of the incident electric field which is parallel to the a ,lane of the output waveguide. Therefore, if the rotation angle 6 is more or less than 90, 'it will cause only r luction in the magnitude of the component being transmitted to the output waveguide. The magnitude the component is proportional to the sine of 0, bone the reduction in output resulting from a variation or 6 from its nominal 93 value is not severe unless the variation is substantial.

With the microwave gyrator 1? available as a phase reversing element as explained above, it follows that several unique switching actions may be obtained from the embodiment shown in Figure 1. For example, power entering arm 5 will be divided in hybrid 6 and appear at arms 7 and 8 as equal in phase components. Now if the length of waveguide section 16 relative to that of sections 17 and 18 for a given direction of current through gyrator coil 22. is made such that the equal components arrive at arms 12. and 13 of hybrid 11 in-phase, the power entering arm 9 will appear at the output of arm 14 of hybrid 11. Then if by means of device 23 the current through gyrator coil 22 is reversed, the equal components will appear outf-phase at arms 12 and 1?: of hybrid 11 and therefore the power entering arm 9 will appear at the output of arm 15 of hybrid 11. Hence it is seen that by selection of the direction of current flow through coil 22, power entering arm 9 may be switched to. either arm 14 or arm 35. it follows that if the direction of current flow through coil 22 is controlled electronically, the switching action of this invention may be made very rapid and may be controlled automatically.

' Utilization of arm of hybrid 6 provides numerous additional properties. For example, power entering either arm 9 or 10 may be switched to either arm 15 or 14. Power entering arm 15 or 14 may be switched to either arm 9 or it). Also, if two separate signals enter arms 9 and 1 3 simultaneously, the two signals will appear simultaneously at arms 15 and 14. Switching the gyrator will interchange these signals between arms 15 and 14. The reverse manner of operation is also possible; that is, signals entering arms 15' and 14 may be interchanged between output arms 9 and 10 upon switching the gyrator. An important characteristic of this circuit is its unilateral nature. Thus, if power which enters arm 9 leaves via arm 14, power which enters arm 14 will not return to arm but will leave via arm 10. Similar unilateral properties apply to the other arms. Many important applications are to be found for such a device. Obviously the unit functions as a very eflicient directional coupler, since power entering arm 9 is directly attenuated in arm 10,

but power reflected from a mismatched terminal at arm 14, will appear in arm 10 only slightly attenuated due to circuit losses. Therefore, the circuit may be used to isolate a source from a variable load impedance. As another application of the circuit, a variable reactive element attached to arm 14 will permit phase control of the output wave at arm 10.

Referring now to Figure 3, a variant embodiment of this invention is shown having still further unique switching functions. In the embodiment of Figure 3, the waveguide section 16 has been replaced by a second gyrator element 25 and connecting waveguide sections 26 and 27. The addition of the second gyrator 25 alters the performance of the device so that the circuit becomes bilateral in nature. For example, if the gyrators are so magnetically biased that power entering arm 9 will leave via arm 14, then power introduced into arm 14 will leave via arm 9, except with a relative phase reversal. Other advantages of this circuit accrue because of symmetry conditions which help to improve bandwidth and stability. As a switch, gyrator 19 might be passive by operating with a fixed, constant magnetic field applied, while switching is accomplished by reversing current in the coil of gyrator 25. With forward or reversed currents in either or both gyrators 19 and 25, bilateral operation, as illustrated above, holds between all arms. Either gyrator may be used to control microwave switching. Thus if under a. given set of conditions, power entering arm 10 leaves arm 15, then reversing the current to either gyrator will cause the power to be switched to arm 14.

In practical circuit assemblies slight compensation may be required in one of the connecting waveguide sections to adjust for initial phase or attenuation unbalance in order that circuit isolation and switching ratios be high.

This is, however, merely a circuit adjustment and hence loss over this band was of the order of 1 db or less.

Figures 4 and 5 illustrate two types of gyrator refinements serving to incorporate within the gyrator circular waveguide portion the E-plane orientation of the input and output connections. While the necessary orientation can be accomplished by twisting one waveguide as shown in Figure 1, it is usually preferable to permit coupling of parallel waveguide sections in order to avoid difficult mechanical design and construction problems in the associated waveguide circuits. The use of parallel input and output waveguides may be easily permitted by incorporating E-plane rotating devices within the gyrator. Either a 45 rotation may be accomplished at each end of the circular guide or a 90 rotation at one end thereof. Two ways of accomplishing the former are shown in Figures 4 and 5.

The Figure 4 arrangement embodies the simplest construction techniques and a conventional gyrator may be easily converted to this arrangement. A series of holes are drilled diametrically through both the metal guide 20 and the dielectric filling 210 at each end of the gyrator. Metal pins are inserted in each of the holes. To aid in showing the position of the pins, the dielectric is not shown in Figure 4. Three holes at each end, as shown in Fig- A second'pin 31 is disposed adjacent to between pins 30 and 32. Pins 33, 34, and 35 are similarly disposed at the right end of the gyrator and further disposed so that the respective outer pins 30 and 33 are parallel and the respective inner pins 32 and 35 are perpendicular. A portion of the circular waveguide section 20 has been cut away so that the position of pins 33-35 inside the guide can be shown.

In the Figure embodiment the pins 30 to 32 and 35 are replaced by twisted metal plates 36 and 37 respectively, disposed with their outer edges parallel and their inner edges perpendicular. Likewise in Figure 5 the dielectric filling is not shown and a portion of section 20 has been cut away. In the Figures 4 and 5 embodiments, the ferrite core, not shown, would be disposed between the innermost pins 32 and 35 of Figure 4 or between the inner edges of plates 36 and 37 in Figure 5.

Although certain specific embodiments of this invention have been herein disclosed and described, it is to be understood that they are merely illustrative of this inention and modifications may, of course, be made without departing from the spirit and scope of the invention as defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A microwave switch comprising, first and second four terminal hybrid junctions, first and second sections of circular waveguide each having a coaxial ferrite core disposed therein, a magnetizing field means associated with each of the ferrite cores for producing a magnetizing field with an orientation and magnitude suitable to cause said cores to rotate the polarization of the electromagnetic energy passing through their respective circular waveguide section, the direction of rotation in each waveguide section being dependent upon the orientation direction of the magnetizing field associated therewith, magnetization control means for at least one of said magnetizing field means operable to reverse the direction of the magnetic field produced thereby, rectangular waveguide sections serially connecting said first circular waveguide between one terminal of said first hybrid junction and one terminal of said second hybrid junction, rectangular waveguide sections serially connecting the second circular waveguide between another terminal of said first hybrid junction and another terminal of said second hybrid junction, waveguide coupling means producing a substantially 90 relation in the orientation of the E-plane of the rectangular waveguides at opposite ends of each of the circular waveguide sections.

2. A microwave switch comprising, first and second four terminal hybrid junctions, first and second sections of circular waveguide each having an electromagnet coil coaxially disposed thereon, a ferrite core coaxially disposed within each of said circular waveguide sections in the magnetic field of its respective coil, means for supplying magnetizing current for said coils of sufiicient magnitude to cause said cores to rotate the polarization of the electromagnetic energy passing through their respective circular waveguide section, the direction of rotation in each waveguide section being dependent upon the orientation direction of the magnetizing field associated therewith, means for reversing the direction of current flow through at least one of said coils, rectangular waveguide sections serially connecting said first circular Waveguide between one terminal of said first hybrid junction and one terminal of said second hybrid junction, rectangular waveguide sections serially connecting the second circular waveguide between another terminal of said first hybrid junction and another terminal of said second hybrid junction, Waveguide coupling means producing a substantially 90 relation in the orientation of the E-plane of the rectangular waveguides at opposite ends of each of the circular waveguide sections.

3. A microwave switch comprising, first and second four terminal hybrid junctions, first and second sections of circular waveguide each having a coaxial ferrite core disposed therein, a magnetizing field means associated with each of the ferrite cores for producing a magnetizing field with an orientation and magnitude suitable to cause said cores to rotate the polarization of the electromagnetic energy passing through the respective waveguide section, the direction of rotation in each waveguide section being dependent upon the orientation direction of the magnetizing field associated with the respective core, magnetization control means for at least one of said magnetizing field means operable to reverse the direction of the magnetic field produced thereby, rectangular waveguide sections serially connecting said first circular waveguide between one terminal of said first hybrid junction and one terminal of said second hybrid junction, rectangular waveguide sections serially connecting the second circular waveguide between another terminal of said first hybrid junction and another terminal of said second hybrid junction and rectangular waveguide coupling means at each end of each of the circular waveguides, each said coupling means producing a substantially 45 rotation of the E plane of its respective rectangular Waveguide section, said 45 rotations being cumulative and reciprocal for each circular waveguide section to effect a relation across each circular section.

4. A microwave switch comprising, first and second four terminal hybrid junctions, first and second sections of circular waveguide each having an electromagnet coil coaxially disposed thereon, a ferrite core coaxially disposed within each of said circular waveguide sections in the magnetic field of its respective coil, means for supplying magnetizing current for said coils of suflicient magnitude to cause said cores to rotate the polarization of the electromagnetic energy passing through their respective circular waveguide section, the direction of rotation in each waveguide section being dependent upon the orientation direction of the magnetizing field associated therewith, means for reversing the direction of current flow through at least one of said coils, rectangular waveguide sections serially connecting said first circular waveguide between one terminal of said first hybrid junction and one terminal of said second hybrid junction, rectangular waveguide sections serially connecting the second circular waveguide between another terminal of said first hybrid junction and another terminal of said second hybrid junction, and rectangular waveguide coupling means at each end of each of the circular waveguides, each said coupling means producing a substantially 45 rotation of the E plane of its respective rectangular waveguide section, said 45 rotations being cumulative and reciprocal for each circular waveguide section to effect a 90 relation across each circular section.

References Cited in the file of this patent UNITED STATES PATENTS 2,532,157 Evans Nov. 28, 1950 2,593,120 Dicke Apr. 15, 1952 2,644,930 Luhrs July 7, 1953 2,650,350 Heath Aug. 25, 1953 2,719,274 Luhrs Sept. 27, 1955 FOREIGN PATENTS 511,649 Belgium June 14, 1952 OTHER REFERENCES Publication II, C. L. Hogan, The Ferromagnetic Faraday Effect at Microwave Frequencies. Bell System Tech. Journal, vol. 31, pp. 22-26, January 1952. (Copy in Div. 16.)

Article, Microwave-Antenna Ferrite Applications, by Sakiotis, Simmons and Chait, published in Electronics (McGraw Hill), June 1952, pages 156, 158, 162 and 166. (Copy in 178-44-1F.) 

